Adjusting focus on Mamiya M645 Super

Discussion in 'Camera Building, Repairs & Modification' started by tkamiya, Mar 23, 2010.

  1. tkamiya

    tkamiya Member

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    I have a Mamiya M645 Super that can use focus adjustment. When focused through prism finder and focused EXACTLY using 2x magnifier, the image isn't actually focused. I did a controlled test today using MIRROR UP and tripod, AND using high-enough shutter speed, it is confirmed that the focus is off enough to be a problem.

    Looking at the lens mount, I know there is a small screw to adjust the resting position of the mirror. But question is.... how the heck do I do this? I can't adjust this with lens on, and I can't possibly detach and attach the lens without disturbing focus. I am guessing, the task is to focus the image on the film plane (by using ground glass instead of film?) and have it focus simultaneously on the view finder, but HOW?

    I have already verified, my focus screen is NOT on backwards. (it is physically impossible on this model)
     
  2. tkamiya

    tkamiya Member

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    By the way, professional CLA is out of question as cost is prohibitive. I am going to use this M645Super as a learning tool and try to do it myself. If I damage it... oh well...
     
  3. suzyj

    suzyj Member

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    I haven't done it myself, but my approach would be to tape some ground glass or a spare focus screen in place of the mirror insert, then put the camera on a tripod and focus on something, then use the MUP lever to pop the mirror up so you can check focus through the back. If adjustment is needed, then pull the lens, adjust the screw a little one way, then repeat the exercise and see if it's better or worse.

    Then repeat until you're happy with it.
     
  4. MattKing

    MattKing Subscriber

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    Are you sure the problem isn't with the focussing screen itself?

    I have never changed the screens on my Mamiya 645s, but I know that they can be swapped with other screens. Someone may have messed up an earlier screen replacement.

    With other cameras, there are sometimes shims used to ensure that the screen is in the right position.

    I would first check the focus at the film plane, to see that infinity focus is correct. If it is, then the problem is with either the screen or the mirror - but most likely the screen.
     
  5. unclemack

    unclemack Member

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    You don't say whether you've owned and used the camera for some time and the fault has just appeared or you've just bought it, but your second post suggests the latter. If you've always used autofocus (I know it's unlikely after 421 posts but this is for other readers too) you may not know that it's important to use the split-image rangefinder correctly - viewing off-axis will give inaccurate results.
    I wouldn't adjust the mirror stop until other possibilities had been eliminated - two faults cancelling each other out isn't ideal.
    First & easiest check is infinity focus at the screen with the split image. A church steeple (or similar, at "infinity" and not through a window), a loupe or a 50mm. lens from a 35mm. camera and a makeshift but flat focus screen on the film rails indicates the degree of error. If one screen is in focus when the lens is at its infinity stop then the other may be where the fault lies.
    Next I would check lens' apparent flatness of field at both screens with the mirror/newspaper test.
    With unfamiliar equipment I spent a lot of time on close visual examination - check the insert, the back and its door, the body, the screen, the lens mount, the lens and the fit of everything looking for clues. Something not quite straight, screws missing or damaged by careless work, rough edges, anything that rattles or feels loose, anything that may have been previously "adjusted" etc. etc.
    I've had cameras for repair with your symptom which have had their mirrors flipped over by unscrupulous sellers. The back of a scuffed mirror looks brand new but throws focus out by the thickness of the glass. The previous owner of my LF reflex viewer had put a brand new and very expensive mirror in - wrong way round. Two minutes to fix.
    Check everything, then adjust the mirror stop if you have to. If you've confirmed the lens' infinity stop is actually at infinity it's easy. Otherwise sticky tape with a sharp pencil line for infinity. Camera on tripod, church steeple, adjust mirror in small increments until split-image aligns.
     
  6. Curt

    Curt Subscriber

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    The interchangeable screens are seated on tiny screws that are factory installed at +/- tolerance. You might consider adjusting the height of the screen to the body, either up or down. The screen must agree with the film plane, when the lens is focused on the screen it must also be in focus on the film.
     
  7. tkamiya

    tkamiya Member

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    Thanks everybody for replies.

    I had this camera for a while and I recently confirmed the problem when I did some test shots under controlled environment. That is, close forcus using 150mm f/3.5 to minimize the depth of focus. I also repeated the test with 50mm f/2.8. I've used manual focus cameras so I am familier with how split screen works and micro prism works. I also used 2x magnifier to ensure exact focus.

    I suspected mirror adjustment be off because if I remove the lens and look into the cavity, I can see bottom of the mirror isn't parallel with bottom of the opening. That is, it's higher on right where the stop is located and lower on the left where it just floats in air. In other words, it is supported on one side only and it's sagging. Looking closely at the stop itself and back of the mirror, I can see some wear.

    Here are some Qs...

    Can I trust infinity focus of the lens? Obviously, this is a mechanical stop within the lens. Over decades, wouldn't they drift due to wear or be affected by expansion/contraction due to temperature?

    I understand there are two focus planes - film and focus-screen. My job is to bring them into agreement. Since I cannot change the distance from lens to film (is this a correct assumption?), all I can adjust is mirror. (is this a correct assumption?) I don't see any ways to adjust the height of focus screen other than using shims. (there isn't any right now)

    What are suitable materials for a temporary focus screen at the film plane? I don't have any spare focus screens.

    Thanks again.
     
  8. John Koehrer

    John Koehrer Subscriber

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    You cannot adjust focus at close distances it has to be infinity.
    I use groundglass at he film plane to check the lens first. If focus is good, but the lens isn't at it's infinity stop, the lens needs to be adjusted. If the lens is at the stop consider the focusing screen. The mirror stop is absolutely the last thing to fiddle with.
    I have seen one camera where the focus was off because the mirror was sitting at an angle, one side of the mirror had come free of it's retaining spring. Look at the mirror, if one side has a small piece of metal on the front surface, the other side should have one too. These are from a spring that holds the mirror into it's frame.
     
  9. unclemack

    unclemack Member

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    Hi, mirror's lower edge at an angle doesn't indicate a maladjustment of the stop but a problem with the hinge mechanism at the top of the mirror or a twisted mirror carrier frame. With the mirror up and the shutter open you may be able to see the cause of the problem in good light with a magnifier. Hold the shutter open with a locked cable release to avoid damaging it.
    Looking at the underside of the mirror through the lens mount and the gate it should be possible to tell if it's horizontal and central, or is skewed in any way.
    If the mirror carrier or hinge mechanism needs straightening remove the mirror first for safety.
    Sorry to repeat myself but don't do anything until you're certain you know the exact cause of the problem.
     
  10. unclemack

    unclemack Member

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    Sorry, got busy, had to go.
    To your specific Q's:
    Inf. stop on the lens is sometimes "beyond" to allow for expansion as you noted.
    Just makes setting the screen easier if it's spot on at the stop. It's not necessary to adjust it though - and you can't do it anyway until you have a screen at the film plane...
    Lens mount rings on cameras are often shimmed to meet specification when new. Common practice in fact.
    Clear, rigid plastic sheet about 2mm. thick can easily be cut to size (about 65 x 42 here I think. Measure your pressure plate on the insert), lightly and randomly sanded one side with 600-grit or finer wet & dry. Used on film rails with sanded side towards lens. If you have a loupe you hold it in place with that. Easy-peasy.
     
  11. tkamiya

    tkamiya Member

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    Thanks.

    Looking into the chamber with a flash light and wiggling the MIRROR_UP knob, it is clear to me that the whole mirror assembly goes up and rests down crocked. Here's something else. As I said earlier, on right side, there is a mirror stop. Also, the right side has the mirror-up assembly. The whole thing depends on right side to move it up and down.

    On left, there is a lever attached to this to move the aperture-close lever on lens. (so that the aperture will close when I release the shutter) I can tell, if I hold this lever by my finger to rel eave the pressure on left side, the whole mirror goes up and down leveled. Looks to me, the design depends on this assembly to keep its shape - and it apparently didn't.

    I've taken this camera apart before and I know for certain, there is no internal linkage going from left to right. (I was careful not to disturb anything else)

    From this, I am thinking, over years of use and uneven mechanical stress has caused this mirror assembly to twist and possibly worn linkage or pivot point.

    Can you help me with few things?

    A lot of alignment procedure depends on lens going to infinity focus. On this lens, it's all the way to right until it stops. How do I know this is actually calibrated correctly? Can it drift? I know, some of modern lens doesn't do this mechanical stop anymore. My Nikon lens actually goes to infinity few degrees before it's mechanical stop. On Mamiya, it's one and the same.

    Another thing is... how do I obtain suitable material so that I can use it to check focus at the film plane?? I do not have spare focusing screen. Are there any commonly available material that's suitable?
     
  12. unclemack

    unclemack Member

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    Hi, I'm sorry but I find it impossible to believe that Mamiya's designers & engineers would produce a mirror pivot assembly completely reliant on a one-sided mount! Early failure would be pre-programmed into such a design.
    I admit I remember the Super less well than other Mamiyas but I feel sure you've missed something here.
    The left mirror box wall where you say there's no connection to the pivot assembly - there is no curved slot? No vestige of a broken or missing lever or pin?
    If the mechanism really is as you describe it - it makes as much sense as a single-seater see-saw.
     
  13. tkamiya

    tkamiya Member

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    There IS a curbed slot on both sides and there are pivot on both sides. There is also a brace under the mirror that reinforces the mirror assembly. The only problem is, the right side is connected to the mirror up knob. Left side is connected to the shutter assembly. The mirror assembly itself acts as a torque bar to move the whole thing up and down.

    Here's another thing. As I said earlier, the mirror assembly rests on a foot that is on the right side. I can easily twist this mirror assembly (gently) to make it straight. As I keep my thumb on the mirror UP knob and try to hold the mirror assembly in mid-air (sort of speak), I can visually see the mirror twist.

    Either way, I can't see how this mirror can rest on one foot and keep it perfectly leveled. Not when it twists this much.
     
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  15. tkamiya

    tkamiya Member

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    There MAY be a hidden linkage somewhere. But the point that I'm trying to make is, I don't see how this thing can rest flat on one side support only. Right now, I'm hesitant to take this a part again. I've taken the cover off the right side to repair shorted flash sync socket. I have not messed with the other side.

    I'd be thankful if you can help me with my Qs on previous post.
     
  16. unclemack

    unclemack Member

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    "Not when it twists this much" is the clue I've been waiting for...
    Many cameras have the lower mirror stop on one side only. I'm looking at a 1000S right now that is the same. It isn't a problem if the upper mirror brackets and pivots are secure on both sides - this is where you need to focus your attention. If left and right upper brackets/pivots can move relative to each other the "tripod" of 2 upper mounts + 1 lower stop is compromised - the mirror carrier is of course the frame of this "tripod."
    The stop-down lever is just that - a simple lever - when the mirror lifts it also lifts the back of the lever and the front of the lever moves down to close the lens diaphragm. It should move easily with the lightest touch of a finger -the stop-down levers on all lenses should also move freely.
    Once you've made the two pivots/brackets and mirror carrier a rigid assembly once again you will still need to check & calibrate infinity focus.
    Good luck.
     
  17. paul ron

    paul ron Member

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    Don't mess with the mirror. The focusing screen gets adjusted to the film plane focusing. As someone stated, using a GG on the film plane see if the screen matches the GG?

    If it does.....

    Perhaps you need a diopter instead? Have you checked your eyes?
     
  18. tkamiya

    tkamiya Member

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    My eyes are fine, thank you....

    With mirror UP, I confirmed that pivot points are fine. They are not lose. Twist that I was talking about is actually caused entirely in the frame that mirror mounts on. I was able to "gently" twist it and put it where they rest nearly parallel to the bottom of the cavity. Not having another unit for comparison is making this process difficult. I'm sure these are not "rock solid" as in can't twist it with any force.

    How is this mirror mounted on this frame? I see 2 tabs on left and 1 tab on right. I don't see any screws to remove these tabs. I can feel, the mirror is not rigidly mounted on the frame. Almost feels and looks as if it has a cushion of some kind between mirror and the frame.

    I made a very flimsy "ground glass" and see that image on prism and GG agree fairly closely but not exactly. At infinity, it's pretty darn close. At close range, it's not that close but still fairly close. I'm going to stop now until I can pickup better loupe and construct much better GG.

    I found else where there are 4 screws that moves the focus screen closer or further from the mirror. I don't know where these screws are and I am not about to start unscrewing indiscriminately. I know there are several black screws under the prism and on both side of the screen (from top of the camera body). 4 of which are almost at the corners of the screen. Are these the one?

    I realize, mirror stop adjustment will not only change the distance but will also change the angle which the mirror sits relative to the lens axis and the focus screen. The height adjustment of the screen will change the distance itself.

    Thanks everybody for help. I'm closer to either fixing or destroying this camera. Time will tell which...
     
  19. Curt

    Curt Subscriber

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    Send it in for a cleaning and inspection.
     
  20. paul ron

    paul ron Member

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    That twist in the mirror is intensional and belongs there. You could have cracked the mirror as so many before you have done and has made me lots of money in the past selling mirrors for $90 a pop, but you were very lucky. Your problem is not the mirror, it's the screen or a diopter that makes the adjsutments. If you don't need one then you certainly need the other.. or both in some cases.

    Yes your eyes are perfect n can see the pubics of a fly, but did it ever cross your mind the wrong diopter is in there from a past owner?... or perhaps the screen was changed n never re-adjusted?

    Leave the mirror alone.. for anyone else messing with a mirror in the future.

    OH be sure to tell the reapir guy you twisted the mirror so he can readjsut it back?






    .
     
  21. unclemack

    unclemack Member

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    Paul, is it possible that the OP was careful rather than just lucky?
    He stated his firm intention to do the work himself whatever the result in his second post.
    Yes, it's irritating and frustrating when equipment is presented for estimate which has been further damaged by users' attempts at repair - but when customers bring these cameras in person do we shout at them? Pour scorn on their efforts?
    The OP should send his camera to you for repair - because you already know that only a simple adjustment is required and therefore your charge for the work will be - what? $50? Sounds like a good deal to me.
     
    Last edited by a moderator: Mar 26, 2010
  22. paul ron

    paul ron Member

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    Lucky is the word, not carefull, most times the mirror cracks when users try straightening it carefully. It's very common that's why I warned him to leave it alone...twice.

    I really don't care what anyone does with their camera, but sheesh, don't ask for advice n disregard it when offered. Also the damge to the frame may be far worse with such force on the delicate internal mirror transport mechanism, even hanging up the govonor.

    No yelling, screaming or scorn... just forcefully urging people to leave it be in bold type. No sence after the fact the damage done n we just add it on to the bill.

    Any repair shop would have done a focus adjustment cheap.
     
  23. ic-racer

    ic-racer Member

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    This is the method I use:

    Measure the lens travel of one revolution of the focus ring, measure the circumfrence. Figure out how much the lens moves in and out for one millimeter of focus ring twisting. Shoot a few frames and "Bracket focus" your target, keep notes on where the focus ring was. Look at the negatives and go back and measure how much you turned the focus ring to get in focus (compared to the finder). Calculate the focus shift. Make a stack of 10 pieces of tape, measure and divide by 10. Then you can figure how many pieces of tape you would need to shim you focusing screen up or down to make it match the film.
     
  24. suzyj

    suzyj Member

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    Paul wrote: "That twist in the mirror is intensional and belongs there."

    How so? As I see it, any twist is going to cause a relative focus shift from one side of the frame to the other. You can shim out the focus screen all you like, and end up with a camera where only the center of the frame matches, and either side are off.

    I think the OP should get the mirror angle right before he tries to adjust or shim anything else.

    I just checked my spare super body (I got a non-functional spare with my super, and sold the super but kept the non-functional body). When the mirror is down, it sits accurately square. When I operate the mirror up knob to lift it, the side on the knob lifts first by a millimetre or so. But importantly, when the mirror drops back down on its stop, it's square.

    Do you want my spare body? It's no good for me, so it's yours for the postage.
     
    Last edited by a moderator: Mar 26, 2010
  25. John Koehrer

    John Koehrer Subscriber

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    I agree with Paul.
    The last thing to futz with is the mirror, at least until ALL other avenues have been tried and eliminated.

    The most common failing will be the focusing screen or the lens barrel/infinity stop slipping. These items are easily adjusted and relatively easily knocked out of adjustment.

    TK, the mirror is usually held to the frame with springs, push them away from the mirror to the side, don't lift them. Some cameras have them glued in & some have small corner retainers that are screwed in.
     
  26. tkamiya

    tkamiya Member

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    I *may* have found the source of my problem.

    Looking very closely at the mirror stop with MUP, I noticed the stop itself is a cam mechanism. I also noticed, the adjustment screw was crocked. Then I noticed, the little cam that this screw goes into is crocked and the little metal tab that this screw pushes against is slightly bent. I then noticed, by carefully moving the mirror stop itself (which itself is another cam), the one with a screw moves, BUT it moves side ways instead of forward and backward. Also, this mirror spot binds as I move it with a tweezers despite the fact it is spring loaded.

    That pretty much means I will not be able to make a reliable adjustment that will stay. If the camera gets bumped and this lever moves somewhat, then it will stay causing recalibration.

    It is hard to say without knowing exactly how these little pieces are mounted, but the fact that one with screw moves sideway bothers me quite a bit. That means whatever the piece this "thing" mounts to or the cam itself is broken - possibly also causing this bind symptom.

    I am all working off of my visual observations. Are there anyone here who has taken this piece apart of know exactly how these cams are put together? (more importantly mounted?)